The present invention generally relates to an optical switching device and, in particular, relates to one such optical switching device having means for selectively changing the polarization of the separated components of an inputted light beam.
The use of optical fibers as a telecommunication and transmission medium has numerous advantages compared to existing telecommunication and transmission media. For example, optical fibers can sustain a broader bandwidth signal and hence can convey larger quantities of information over the same period of time than existing media. Further, light waves are shorter than the conventional microwaves commonly used in existing telecommunication systems and thus a substantial reduction in the physical size of components is readily achievable. This further results in a cost reduction for materials, packaging and manufacturing. Still further, current optical fibers exhibit little or no electromagnetic radiation or radio frequency radiation thus resulting in negligible impact on the surrounding environment. In addition, fiber optics are relatively insensitive to radio frequency interference from surrounding devices or systems.
To be viable, every telecommunication system must include some means for controllably redirecting a signal, or at least a portion thereof, to or from a transmission media or between one or more such medium. In the case of an optical telecommunication system the preferred means is an optical switch. Currently, optical switches are generally mechanical in nature.
However, mechanical switches require relatively high driving power and are subject to wear, abrasion and fatigue. As a result, mechanical switches are prone to failure after repeated use. In addition, since a rather small optical fiber is usually displaced from alignment with one port fiber into alignment with another port fiber, mechanical switches can easily become expensive. One particular reason for this expense is the very small tolerances required to ensure the proper alignments between the optical fiber moved and the optical fibers of the ports.
Recently, liquid crystal optical switching devices have been proposed as an alternative to mechanical switches. Typical of liquid crystal optical switches proposed to date are those described in U.S. Pat. No. 4,201,422 issued to McMahon et al. on May 6, 1980, U.S. Pat. No. 4,278,327 issued to McMahon et al. on July 14, 1981, and U.S. Pat. No. 4,385,799 issued to Soref on May 31, 1983. Therein, a plurality of liquid crystal switch designs are described wherein optical fibers are attached to the side angled surfaces of a pair of opposing trapezoidal prisms. The trapezoidal prisms are arranged with the bases thereof parallel and with liquid crystal material positioned therebetween.
Although the optical switches described in these references have some advantages over mechanical switches, specifically no moving parts, these liquid crystal switches are both difficult to manufacture and expensive since all the surfaces of the trapezoidal prisms must not only be optically flat, but be fixed at a precise angular relation to each other. As a result, the liquid crystal optical switches, as described in the above references, are presently impractical for optical communication systems.
Consequently, since a typical telecommunications network may include hundreds, it not thousands, of switching devices, a low cost, readily manufactured optical switching device is needed in order to more fully realize the advantages of an optical telecommunication system.